(a) Field of the Invention
The present invention relates to a location tracking apparatus and method. More specifically, the present invention relates to an apparatus and method for tracking three-dimensional locations of a mobile station used for mobile communication systems.
(b) Description of the Related Art
With the progress of mobile communication systems, persistent attempts have been made to utilize mobile communication networks in a variety of fields as well as the existing voice telephone communication and data services. In addition, various location tracking methods have been reported for using location information in providing position-based services such as emergency rescue, vehicle tracking, searching for missing children, and the like.
The GPS (Global Positioning System)-based tracking technology is an example of the location tracking methods. The GPS-based tracking technology that uses location information sent from four GPS satellites moving around the earth for representation of the current location is known to provide very precise location information. However, this technology requires a separate GPS receiver of which the price rises in proportion to the precision of location tracking, and is thus unsuitable for use in tracking services using wireless telephone networks.
Another method for tracking the location of a mobile station is based on triangulation technology. FIG. 1 shows a cell structure of a mobile communication system for explaining a location tracking method using triangulation technology in accordance with prior art.
In the mobile communication network that has a cell structure centering on base stations, a mobile station receives signals from at least three base stations a, b, and c, and determines its relative location with respect to each base station using the base station""s coordinate and signal-sending time. However, this method requires precise time synchronization among the base stations for the mobile station""s measuring of a precise time of arrival of the received signals, and it demands that the individual base stations increase the power of the output signals for the mobile station""s acquiring of the signals simultaneously from the at least three base stations.
To overcome this problem in regard to synchronization and efficiency, methods have been proposed for tracking the location of a mobile station using a single base station.
For example, U.S. Pat. No. 6,300,905 discloses a method for tracking the location of a mobile station using a single base station in the CDMA (Code Division Multiple Access) and TDMA (Time Division Multiple Access) systems. In the method, the single base station measures the mobile station""s RF forward link signal and the propagation-delay time to calculate the distance to the mobile station, and utilizes at least three multiple sector antennas to measure the mobile station""s azimuth angle.
U.S. Pat. No. 6,252,867 discloses a method for tracking two-dimensional locations of a mobile station using a single base station in the CDMA system having a multiple channel structure. The base station in this method also uses the propagation-delay time to obtain the distance to the mobile station, and it measures the mobile station""s azimuth angle using a plurality of phased array antennas.
Though only a single base station is used in tracking of the mobile station""s location, neither of the methods can provide three-dimensional location information while considering the altitude of the mobile station, but only two-dimensional location information such as distance and azimuth angle. The methods also have a problem in that the resolution and precision of angle measurements are dependent on the number of antennas.
It is an object of the present invention to provide an apparatus and method for tracking a mobile station""s precise three-dimensional location information simply by using a single base station in a mobile communication system.
In one aspect of the present invention, there is provided an apparatus for determining the location of a mobile station that includes: a beam-forming antenna for receiving a signal from the mobile station; a distance detector for measuring the distance between a wireless base station and the mobile station from the signal received by the beam-forming antenna; an azimuth angle detector for measuring an azimuth angle of the mobile station with respect to the wireless base station by horizontal scanning of the beam-forming antenna; an elevation angle detector for measuring an elevation angle of the mobile station with respect to the wireless base station by vertical scanning of the beam-forming antenna; and a location determiner for calculating the output signals of the distance detector, the azimuth angle detector and the elevation angle detector, determining the location of the mobile station and updating it.
The distance detector includes a time-distance detector for measuring the propagation-delay time of the signal received by the beam-forming antenna and calculating the distance between the wireless base station and the mobile station from the propagation-delay time, and/or a power-distance detector for measuring the power of the signal received by the beam-forming antenna and calculating the distance between the wireless base station and the mobile station from the power.
After determining an initial location of the mobile station, the location determiner continues to receive information about the mobile station""s distance, azimuth angle and elevation angle at regular time intervals, takes the respective averages of the distance, the azimuth angle and the elevation angle and updates the location of the mobile station based on the averages.
In another aspect of the present invention, there is provided a method for determining the location of a mobile station, by which at least one wireless base station including a beam-forming antenna for generating an antenna beam in multiple directions determines the location of the mobile station, the method including: (a) receiving a signal from the mobile station; (b) calculating the distance between the wireless base station and the mobile station from the received signal; (c) scanning the antenna beam of the beam-forming antenna in a horizontal direction; (d) determining a first position of the beam-forming antenna at the peak power of the received signal during the horizontal scanning, and measuring an azimuth angle between the initial position of the beam-forming antenna and the first position; (e) scanning the antenna beam of the beam-forming antenna in a vertical direction; (f) determining a second position of the beam-forming antenna at the peak power of the received signal during the vertical scanning, and measuring an elevation angle between the initial position of the beam-forming antenna and the second position; (g) putting the distance, the azimuth angle and the elevation angle together to acquire an initial location of the mobile station; and (h) updating the acquired initial location of the mobile station at regular time intervals.
The distance calculation step (b) includes measuring the propagation-delay time of the received signal and calculating the distance from the propagation-delay time; or measuring the power of the received signal and comparing it with the power of a signal sent from the wireless base station to calculate the distance.
The location updating step (h) includes taking the respective averages of the distance, the azimuth angle and the elevation angle for a predetermined time interval and determining the location value of the mobile station as the averages.